Ethylbenzene hydroperoxide can be prepared by the liquid phase oxidation of ethylbenzene with oxygen containing gas, such as air. Such oxidation processes are well known in the art. An example thereof is described in U.S. Pat. No. 5,883,268.
In such oxidation reaction of ethylbenzene, methyl phenyl carbinol (1-phenylethanol) and methyl phenyl ketone (acetophenone) are formed as side-products. Subsequent oxidation of an alkene (such as propene) with the ethylbenzene hydroperoxide results in the production of alkene oxide (an oxirane or epoxide; such as propylene oxide) and methyl phenyl carbinol. Methyl phenyl ketone can be converted with hydrogen into methyl phenyl carbinol. Methyl phenyl carbinol can be dehydrated into styrene. Both the styrene and the propylene oxide are valuable market products.
Processes for the joint preparation of styrene monomer (“SM”) and propylene oxide (“PO”) are known in the art and are commonly referred to as “SM/PO” processes. An SM/PO process is for example described in WO 00/05186. In general, an SM/PO process comprises the steps of:    (a) reacting ethene and benzene to form ethylbenzene,    (b) reacting ethylbenzene with oxygen containing gas to form ethylbenzene hydroperoxide,    (c) reacting ethylbenzene hydroperoxide with propene in the presence of an epoxidation catalyst to form propylene oxide and 1-phenylethanol, and    (d) dehydrating 1-phenylethanol into styrene in the presence of a suitable dehydration catalyst.
During said steps (b) and (c), methyl phenyl ketone is formed as a side-product. Prior to said step (d), this methyl phenyl ketone may be converted with hydrogen to methyl phenyl carbinol (1-phenylethanol).
During said step (b) of oxidising ethylbenzene into ethylbenzene hydroperoxide, not all ethylbenzene reacts. Said unreacted ethylbenzene may be recycled to the oxidation reactor. The oxidation reaction is carried out at a concentration below 20 wt. % of ethylbenzene hydroperoxide on the basis of the total weight of the reaction mixture. In general, at or above this concentration, the production of the side-products methyl phenyl carbinol and methyl phenyl ketone grows relative to the amount of ethylbenzene hydroperoxide, causing inefficient loss of reactant ethylbenzene.
Hence, the concentration of ethylbenzene hydroperoxide in the reaction mixture is kept relatively low. There is a continuing desire among those skilled in the art to achieve a high oxidation rate when working under the above maximum ethylbenzene hydroperoxide concentration.